1. Field of the Invention
The present invention concerns a chain saw provided with a lubrication device for the guide bar/cutting chain assembly. It also deals with the method implemented for performing this lubrication.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Such tools with cutting chains, commonly called chain saws, are well known and are commonly used to cut up various materials (wood, concrete, bricks, tiles etc.). They include a cutting device constituted by an endless cutting chain mounted so as to turn around a drive sprocket and a chain guide generally of an oblong shape and equipped with a peripheral guide rail and a power source (for example constituted by a combustion engine or an electric motor) performing the drive of this chain, through the intermediary of said sprocket.
For the proper operation of a tool of this kind, it is indispensable to ensure efficient lubrication between the guide bar and the cutting chain in order to reduce the friction generating heat, loss of efficiency, accelerated wear and over-consumption of energy.
For this purpose, a lubrication fluid is stored in a tank where it is picked up before being directed, over an appropriate conduit, towards the guide bar/cutting chain assembly. The transmission of the lubrication fluid to the guide bar/cutting chain assembly is generally performed through the intermediary of a pump. It is sometimes obtained by gravity (not very efficient) or by pressurizing the storage tank (difficult dosage because it depends on the pressure and varies accordingly).
When the lubricating fluid is transported to the guide bar/cutting chain assembly by a pump, which is most often the case, this pump and the cutting chain are driven by the same motor or engine. Lubrication of the chain is then performed constantly and proportionally to the rotational speed of this motor or engine which leads to significant consumption of the lubricating fluid, without being necessarily always adequate for particularly difficult operating conditions which accompany a braking of the chain and a slowing down of the engine or motor, and consequently less lubrication of the chain.
The document FR 2 505 719 describes a device of this kind. According to this document, the electro-magnetic lubricating pump of the chain saw is actuated by the combustion motor driving the chain of the chain saw, through the intermediary of a magneto and a micro-calculator.
More concretely, with the current lubrication methods and systems, proper dosage of the quantity of oil taken from the tank is difficult because the output of the pump increases with the rotational speed of the engine and can lead to the useless delivery of too large volumes of oil. Furthermore, since this speed is reduced when more force is required for the cut, one reduces also the quantity of oil delivered to the chain when this is the moment where good lubrication would be necessary in order to reduce overheating and wear.
The invention aims at least at improving the efficiency of the lubrication of the guide bar/cutting chain assembly of chain saws and their drive sprocket by reducing the consumption of lubricating fluid and avoiding splashing the operator which happens frequently and causes stains and burns.